the reason there arent relays is that theyre expensive to run (150$+ a month, if you rent, and the cost seems to scale linearily with the amount of users on the network), i saw a blog about someone who hosted one briefly (https://whtwnd.com/bnewbold.net/entries/Notes%20on%20Running%20a%20Full-Network%20atproto%20Relay%20(July%202024), and it isnt even that hard to setup, it's mostly just the cost.

Also, relay's aren't technically needed, you could make an appview that pulls from pds's directly.